Why it fills up so mysteriously

A free Google account comes with 15 GB, and that allowance is pooled across three services:

So you can be diligent about Drive, never upload anything, and still hit the limit — because three years of phone videos went into Photos, or because a decade of newsletters with PDF attachments sits in Gmail. The warning you see is usually raised by whichever service you happened to be using, which is why the message often points at the wrong place.

See the breakdown first

Before deleting anything, look at where the space actually went. Go to one.google.com/storage. You don't need a paid plan to use this page.

It shows a bar split by service, and — more usefully — a storage manager that surfaces the specific things worth clearing: large emails with attachments, items sitting in trash, large files in Drive, and unsupported videos that can never be played. Working from that list is far more efficient than scrolling through folders guessing.

Whatever the biggest slice is, start there. Deleting 400 small documents from Drive when Photos is using 11 GB is wasted effort.

Gmail: the search terms that find the big stuff

Almost all Gmail storage is attachments, not text. Paste these into the Gmail search box:

SearchWhat it finds
has:attachment larger:10MEvery email with an attachment over 10 MB — usually the top of your list
larger:25MThe genuine monsters. Often a handful of emails worth hundreds of megabytes
has:attachment older_than:3yOld attachments you'll almost certainly never open again
in:spamSpam still counts toward your quota until it's purged
in:trashSo does the trash
from:noreply larger:1MAutomated mail with heavy attachments — statements, receipts, reports

Sort through the results, save anything you want to keep (download it, or move it to a computer), then delete. Two things people forget:

Photos: usually the largest share

For most people, Google Photos is the biggest consumer, and video is the reason. A few minutes of phone video can outweigh a thousand photographs.

Check your backup quality setting

In the Google Photos app, open your profile picture → Photos settings → Backup and look at the upload quality. "Original quality" uploads files at full size. "Storage saver" compresses them, which for phone photos viewed on phone screens is a difference most people never notice — and it consumes considerably less space.

Changing this affects future uploads. Google has at times offered a tool to recompress existing originals to storage saver, which can recover a large amount of space in one action; look for a "recover storage" option in the same settings area. Note that this is not reversible — the original-quality versions are replaced.

Clear the two hidden piles

Delete the categories you don't need

Search your library for screenshots. Most people have thousands, and almost none are worth keeping. The same goes for burst shots, blurry duplicates, and downloaded images from messaging apps. Google Photos' own storage manager flags large videos, blurry photos, and screenshots as suggestions — that list is a genuinely good place to start.

Before you delete anything

If a photo exists only in Google Photos, deleting it there deletes it everywhere. Download anything irreplaceable first — Google Takeout can export your entire library as an archive. Do the export, confirm the files actually open, and only then start clearing.

Drive: large files and the trash trap

In Drive, use the Storage view in the left sidebar (not "My Drive"). It lists every file you own sorted by size, which is exactly what you want and is not the default view anywhere else.

Then:

What doesn't count against you

Useful to know, so you don't waste time deleting the wrong things:

Also worth knowing: a personal Google account that goes completely unused for two years may have its content removed under Google's inactivity policy. If you keep a spare account purely as an archive, sign into it occasionally.

What happens if you stay full

Once you're over the limit, several things stop working, and not all of them are obvious:

You keep access to everything already there — nothing is deleted for being over quota in the short term — but the account becomes read-only in practice.

If you'd rather not spend the afternoon deleting

Two legitimate alternatives to a cleanup:

Whichever you choose, do the storage-manager review first. Knowing that 9 GB of your 15 is old video from a phone you no longer own changes the decision.